The foco theory of revolution by way of guerrilla warfare, also known as focalism, was formulated by French intellectual and government official Régis Debray, whose main source of inspiration was Marxist revolutionary Ernesto "Che" Guevara's experiences surrounding his rebel army's victory in the 1959 Cuban Revolution.
Its central principle is that vanguardism by cadres of small, fast-moving paramilitary groups can provide a focus for popular discontent against a sitting regime, and thereby lead a general insurrection. Although the original approach was to mobilize and launch attacks from rural areas, many foco ideas were adapted into urban guerrilla warfare movements by the late 1960s.